Dont listen to any of those trolls. On high elo, you gotta rush Zhonya's hourglass, because when you ult, you will get instafocused and instakilled. Also as colehaffner said, go jungle, or dont play fiddle. Fiddle in the middle sucks ass.

Anyone can counter you as fiddle. He's verry squishy and he doesnt have any escape mechanism. Also...silence doesnt stop bursters like Cassiopeia, Veigar, Xerath etc.
In ranked, you will always get countered. Only fev champions which fiddle counters are Twisted Fate, Ryze, Annie, and thats just because of their short range.

Gameplay-wise, you're quite weak when you attack enemies head on. If you're trying to gank, try to be sneaky, don't rush an opponent but wait for the laner to engage. In teamfights, don't run in, but try to wait until your tanks have made the initiation before you charge your ultimate.

Above all, do not try to be a hero with fiddlesticks. He's a squishy ************ .

Skill-wise, I always found it rather difficult to find a proper leveling order, but try to keep drain a low level and fear high. Alternate leveling fear and Dark Wind, keep drain at level 1 or 2 max.

Doran's ring is a good item to start with
If you want to deal higher damage quickly, you can get a Rabadon's Deathcap soon
Rylai's Crystal Scepter is an amazing item as it gives you more health, some ap, and an amazing passive (It applies a 35% slow to enemies affected by drain on every single hit of drain).
Always get a Zhonya's Hourglass (though not as the first item). The armour is good, so is the ap, but what you really want is the active. Crowstorm continues through the invincibility, so you can crowstorm into a bunch of enemies, activate Zhonya so you can't get harmed, and hope your team comes in to help. Or you can turret dive enemies with low health. The uses are unlimited.
They say spellvamp items (Hextech Revolver and Will of the Ancients) are good, but I don't really see much of a change. The like 80% or something spell vamp of drain should be enough.
Abyssal Scepter (I think that's the name) gives magic resist and some ap, plus a similar effect to your passive but twice as powerful.
Rod of Ages makes you less squishy early game, but I don't really like it.
Void Staff is great if the enemies are building magic resist.
If you don't die much (and kill quite a lot of people), Mejai's Soulstealer would be good. However, it is probably a bad idea to buy it, as you will be targeted by enemies right away if you get decent stacks. Besides, your first Rabadon's Deathcap gives you more ap with it's +30% ap passive.